Dehydrogenation process

ABSTRACT

A process and apparatus for the catalytic conversion of hydrocarbons which are especially suited for the dehydrogenation of long chain normal paraffins. The reactants pass through a radial flow catalyst bed and immediately impinge upon a cylindrical indirect heat exchange means in which the feed stream to the process is circulated as a cooling media, and the reactants then pass into a contact condenser located within the heat exchange means. A cooled stream of liquid reactor effluent is charged to the contact condenser to effect a condensation and separation of the reactants from the recycle gas within the reactor.

United States Patent Winter, III et al.

[4 1 Sept. 23, 1975 DEHYDROGENATION PROCESS 2.433.670 12/1947 Kropp23/288 K 2.548.015 4/1951 Goodson t al. 208/146 [75] Inventors: Pf wmte"mxDes Flames; 2.981.677 4/1961 B6w1e$..... 1. 208/146 wllllam Arlmgmn2.989 53 6/196] Gilmore 62/11 Heights, both of ill.

[73] Assignee: Universal Oil Products Company, Primary Emminer HeTbcftLevine D Fl m [[1 Attorney. Agent, or FirmJames R. Hoatson, Jr.; RobertW. Erickson; William H. Page, ll [22] F1led: Mar. 14, 1974 [2l] Appl.No.: 451,660 [57] ABSTRACT Related U.S. Application Data A process andapparatus for the catalytic conversion [63] Continuation-impart of Ser.No. 30l,0()7, Oct. 26 of hydrocarbons which are especially Suited fm the1972 b d dehydrogenation of long chain normal paraffins. The reactantspass through a radial flow catalyst bed and [52] U.S. Cl. 208/146;23/288 R; 23/288 K; immediately impinge upon a cylindrical indirect heat208/100; 260/6833 exchange means in which the feed stream to the pro ClClOg 23/00; ClOg 35/00 cess is circulated as a cooling media. and thereactants [58] Field of Search 208/146, 100, 147; then P into a Contactcondenser located within the 23/288 R 288 K heat exchange means. Acooled stream of liquid reactor effluent is charged to the contactcondenser to ef- [56] References Cited feet a condensation andseparation of the reactants UNITED STATES PATENTS from the recycle gaswithin the reactor.

2,391,315 l2/l945 Hulsberg .4 23/288 K 13 Claims, 1 Drawing Figure 27-2' 28- i Cara/ys! Recycle /7 Gas fgg Healer 35 Paraffin Charge l Stream7 'Heal Exchange Tubing I Ton/ac! Condenser Rad/a! Flow 1 Ca/a/ys/ Bed 5l Coo/er To Product Stripper US Patent Sept. 23,1975

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Q mmau uxm ut w w m 3 E3 Al xxb b DEHYDROGENATION PROCESS CROSSREFERENCE TO RELATED APPLICATION This application is aContinuation-ln-Part of our copending application entitled Radial FlowReactor With Indirect Heat Exchange, Ser. No. 301,007, filed Oct. 26,1972 now abandoned, all the teachings of which application areincorporated herein by this specific reference thereto.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionpertains to a process for the conversion of hydrocarbons, and moreparticularly to a process for the dehydrogenation of long chainparaffins to monoolefins. The invention also pertains to aradial flowreactor apparatus for the conversion of hydrocarbons which contains anindirect heat exchange means and a contact condenser. The processeffects the heat exchange, condensation and phase separation of thecatalyst bed effluent stream within the reactor.

2. Description of the Prior Art Processes for the catalyticdehydrogenation of paraffinic hydrocarbons are well known in the art,with specific examples being shown in US. Pat. Nos. 3,448,165 and3,448,166 (Cl. 260-6833).

Using an indirect heat exchange means within a reactor is shown by US.Pat. Nos. 2,433,670 and 3,753,662 (Cl. 23-289). The latter utilizes thismeans to cool a reacting gas to promote further reaction in a subsequentcatalyst bed in a process governed by thermodynamic equilibrium.

As larger volumetric throughputs of reactants are being designed for,the diameter of the reactors used in high space velocity dehydrogenationprocesses has been steadily increasing. The resulting problems caused bythe long residence time of the chemically unstable olefins within thecenterpipe volume has been a subject of concern in the art. Theseolefins tend to polymerize and decompose resulting in lower yields fromthe process. US. Pat. No. 3,620,685 discloses the use of an invertedthumb-like structure to fill this centerpipe volume and to therebyquicken the flow of the heated reactants from the reactor and into anexternal heat exchanger.

The use of a contact condenser in which a portion of the condensedmaterial is cooled and then returned to cause the condensation of ahydrocarbon containing stream being fed to the condenser is shown in US.Pat.

' No. 2,989,853 (Cl. 62-11).

A method for quickly changing the catalyst within an isomerizationreactor is presented in US. Pat. No. 3,299,155. The total spent catalystloading is removed from the bottom of the reactor and fresh catalyst isadded at the top of the reactor.

BRIEF SUMMARY OF THE INVENTION Our invention provides a reactor for thecatalytic conversion of hydrocarbons, which comprises a verticallyorientated, cylindrical enclosed outer vessel; two verticallyorientated, concentric, cylindrical catalyst retaining screens locatedwithin the outer vessel; an indirect heat exchange means located withinand adjacent to the innermost catalyst retaining screen; and a contactcondensing means located within the indirect heat exchange means. Ourinvention also provides a process for the catalytic conversion ofhydrocarbons which comprises the steps of passing a vaporized feedstream into a radial flow reactor and inward through a cylindrical bedof solid catalyst; contacting the effluent of the catalyst bed with acylindrical heat exchange means located within the reactor to effect acooling of the effluent; and passing the effluent into a contactcondensing means located within the reactor to effect a partialcondensation and a separation of the effluent into a vapor stream and aliquid stream which are separately withdrawn from the reactor.

DESCRIPTION OF THE DRAWING The drawing depicts the preferred embodimentof our invention, which is its utilization for the dehydrogenation oflong chain normal paraffins. It is not so limited however, and variousmodifications to conform to varying processing conditions andalternative hydrocarbon conversion processes are still within the scopeof the appended claims.

A liquid feed stream of normal paraffins enters the process through line1 and is mixed with a recycle gas stream in line 2 to form a combinedfeed stream flowing through line 3. The combined feed stream enters acircular distribution duct 4 located on the outer vessel 11 of thereactor. The inlet side of duct 4 distributes the combined feed streamto the inlet sides of the large number of hairpin heat exchange means 5which form a cylinder within the reactor. The combined feed streamtherefore flows down the inner side of the heat exchange means and upthe outer side to maximize heat transfer and then returns to thecollection side of duct 4. The now warmer combined feed stream leavesduct 4 via line 6 and passes into a fired heater 7. A now completelyvaporized combined feed stream leaves heater 7 through line 8 and splitsinto different portions which enter the outer vessel 11 through lines 9and 10.

The combined feed stream disperses into an annular distribution volume36 on the inside of the cylindrical wall of outer vessel 11 and thenpasses inward through the outermost catalyst retaining screen 12. Theheated combined feed stream then contacts an annular bed ofdehydrogenation catalyst 13 located between catalyst screens 12 and 12'.A disc-shaped fiow directing plate 14 seals off the bottom of theannular distribution volume to prevent reactants from by-passingcatalyst bed 13. In a similar manner, a disc-shaped flow directing plate35 seals off the top of the reactant distribution volume. The feedstream undergoes at least a partial conversion in the catalyst bed andexits through the innermost catalyst retaining screen 12' as an effluentstream which soon contacts the heat exchange means 5. This catalyst bedeffluent stream is prevented from by-passing the heat exchange means bya second flow directing plate 15 located at the bottom of the heatexchange means.

The catalyst bed effluent then enters a contact condenser 20 wherein thelong chain hydrocarbons in the catalyst effluent are cooled andcondensed to form a liquid phase which accumulates in the bottom ofouter vessel 11 and is removed through line 21. A volume of the liquidphase will be retained within the cylindrical wall 37 to activate a flowcontrol means in line 21. The remaining uncondensed gases are furthercooled as they pass upward through the contact condenser to the top ofouter vessel 11 where they are removed in line 27. A part of these gasesapproximately equal to the net hydrogen production in the process isremoved via line 28 and the remaining portion is utilized as the recyclegas stream in line 2. This recycle gas stream is pressurized incompressor 29 and returned to the process. The liquid phase withdrawn inline 21 is divided into a first portion passed to a product stripperthrough line 26 and a second portion which enters line 22 and ispressurized in pump 23. This second portion is then passed through acooler 24 and returned to the outer vessel through line 22. In thecooler, this second portion is cooled sufficiently to provide the neededcondensation of the catalyst bed effluent. It is then distributed overthe contact condenser by a liquid distributor 25. This cooled liquidflows downward countercurrent to the rising gases to provide efficientcondensation of essentially all the heavy hydrocarbon material in thereactor effluent.

When it is necessary to replace the catalyst held between annularcatalyst retaining screens 12 and 12, a number of valve meansrepresented by valves 19 and 19' are opened and the catalyst'is allowedto drain into a receiving vessel through a plurality of catalystwithdrawal conduits represented by 18 and 18. Valves 19 and 19 are thenclosed and valves 17 and 17' are opened to allow fresh catalyst to enterthe outer vessel 11 through a plurality of catalyst transfer conduitsrepresented by lines 16 and 16'. The catalyst transfer conduits areequally spaced around the periphery of the outer vessel to allowcomplete and uniform removal and replacement of the catalyst.

DETAILED DESCRIPTION Radial flow reactors are used in many petroleum andpetrochemical conversion processes, including such processes asreforming, the isomerization of normal paraffins, the isomerization ofalkyl aromatics, the hydrodealkylation of aromatic hydrocarbons, theconversion of benzene to cyclohexane and the dehydrogenation of longchain normal paraffins to the corresponding mono-olefin. Many of theseprocesses are favored by the use of a low-pressure within the reactionzone, and currently such processes operate at a rather limited degree ofconversion per pass over the catalyst. The combination of these factorsresults in a very large reactant flow rate at pressures of from about 15to 200 psig.

The relative percentage of the total operating cost of these processeswhich may be attributed to the recirculation of the reactants and othergases increases as the pressure of the process is lowered. As anexample, in some large low pressure plants, a difference of 1 psi. overa reactant recirculation loop will increase net pumping cost by $25,000per year. It is therefore very important that all pressure drops beminimized, and it is therefore an objective of our invention to providea reactor and a process whereby low pressure, high space velocity,catalytic hydrocarbon conversion processes may be performed with a lowpressure drop through the process and the reactor.

In petrochemical processing, and particularly in the dehydrogenation ofnormal paraffins, there are a number of undesirable side reactions whichoccur when the reactants are held within the reactor at the elevatedtemperature and not in contact with the catalyst, a condition referredto as thermal time." An example is the decomposition of olefins todiolefins and the formation of aromatic compounds. The ultimate effectis a decrease in the selectivity of the process and a lower return oninvested capital. When the desired contact time of the reactants withthe catalyst is very short, it is necessary to limit the catalyst torelatively thin layers. As larger volumetric throughputs of reactantsare being designed for, the inner diameter of the reactor is increasedso that maximum quantities of feedstock can be treated per unit time ina single reactor. Large centerpipe volumes are created in this manner.The centerpipe volume of a reactor ,is defined to be the volume within aradial flow reactor which is located inside of the innermost catalystretaining screen. The lengthy thermal times within these largecenterpipe volumes increases the undesirable side reactions, such as thepolymerization of chemically unstable olefins, and therefore degradesthe catalyst bed effluent. Rates of many chemical phenomena includingthe undesired side reactions are exponentially dependent on the absolutetemperature of the reactants. Therefore, it is desirable to have thethermal time be as short as possible. It is therefore also an objectiveof our invention to reduce the thermal time within a radial flowreactor.

A remedy which has been proposed to reduce the thermal time is the useof an inverted thumb-like structure to fill the centerpipe volume and tothereby shorten the time required for the heated reactants to go fromthe reactor to an external heat exchanger. This however increases thepressure drop in the reactor. The present invention is an improvementover the prior art in that it reduces the net pressure drop in theprocess and also provides a means for quickly quenching the catalyst bedeffluent. The effluent stream is also condensed and separated into gasand liquid effluent streams within the reaction vessel. Therefore, thepresent invention is also an improvement over the prior art in that itreduces the net capital costs of constructing such a process. The outervessels and the connecting piping for the effluent-feed heat exchanger,the other heat exchangers used for cooling the reaction zone effluentand the vessel normally used to separate the catalyst bed effluent intoseparate gas and liquid streams are no longer required.

The sequential steps of heat exchanging a feed stream with the reactoreffluent stream, further heating the feed stream and passing it throughthe reactor, and then cooling and separating the reactor effluent arefound in a'sizable fraction of all catalytic petrochemical and petroleumrefining processes. Regardless of the desired reaction, the neededcapital expenditures and the continuously required utilities cost ofoperating the process are important to its profitable operation. Oneobjective of our invention is to provide a process and a reactor for theperformance of any of these processes which results in the reduction ofthe cost of construction and the cost of operation of theseprocesses. Inaccordance with this objective, our invention provides a process whereinthe catalyst bed effluent stream of a radial flow reactor is contactedwith an indirect heat exchange means located within the radial flowreactor and arranged in a cylindrical pattern adjacent to the innermostcatalyst retaining screen, and the catalyst bed effluent stream is thenpassed into a contact condensing means located within the radial flowreactor to effect a'partial condensation and a separation of thecatalyst bed effluent stream into a vapor phase stream and a liquidphase stream which are separately withdrawn.

The apparatus in which our process is practiced is normally containedwithin a vertically oriented, cylindrical, sealed outer vessel having aclosed top and bottom and numerous openings for the passage of variousprocess streams. To aid in the description of its construction, theouter vessel may be divided into an upper portion and a lower portion,which comprise respectively the top and bottom half of the vessel. Asused herein, terms such as innermost or inward are meant to be inreference to the central axis of the reactor and respectively refer to aplacement or direction closer or toward the axis. The dominate internalstructures contained within the outer vessel include the two or morevertically oriented, concentric, cylindrical catalyst retaining screens.These screens form an annular reactant distribution volume between theinner wall of the outer vessel and the outer surface of the outermostcatalyst retaining screen, and they also form an annular catalystretention volume between the catalyst retaining screens. Three catalystretaining screens may be used to form two catalyst retention volumeswhen it is desirable to load the reactor with two types of catalyst orwith a bed of adsorbent material before or after a bed of catalyst. Itmay also be desirable to have four catalyst retaining screens within thereactor to provide a void space between two catalyst retention volumes.This situation could arise when it is necessary to either heat or coolthe reactants between sequential passes through catalyst beds or when itis desired to add additional portions of one or more reactants or to adda different reactant to the effluent of a first catalyst bed. In thesesituations, it is contemplated that there will be other structures suchas heating coils or heat exchange means or reactant distribution meanslocated in a void annular volume between the second and third screensinward. In a typical commercial paraffin dehydrogenation reactor, thecatalyst bed may be approximately to 60 centimeters thick and thecenterpipe volume may be approximately 1.8 to 4.6 meters across and 6 ormore meters high. The construction of these catalyst retaining screensis not critical to the concept of the invention, and they may comprisesolid perforated plates, a fine screen material covering largeperforations in a solid plate, or any form of slits or openings betweenhorizontal or vertical windings of flat metal or wire-like conduit. Itis preferred that the catalyst retaining screen comprise a multitude ofparallel, vertical, wedge shaped bars having their widest portion facingthe catalyst. The catalyst retention screens may or may not have a solidportion at their top and bottom to prevent the flow of reactants aroundthe porous portion of the screen. If present, the solid portion may befilled with either inert material such as alumina balls or withadditional catalyst to allow for the settling of the catalyst containedwithin the catalyst bed.

After passing through the catalytic material, the reactants emerge fromthe innermost catalyst retention screen as a catalyst bed effluentstream and impinge upon an indirect heat exchange means. The overallshape of the indirect heat exchange means must resemble a verticallyoriented hollow cylinder. This provides a cylindrical central voidvolume in which to place the contact condensing means. However, itsexact shape, size or construction is not a limiting factor, and it maycomprise anything from the circular array of U-tubes shown in thedrawing to a plate-type exchanger or a spiral or circular grid of heatexchange tubes. The heat exchange tubes themselves may of course havefins either mechanically attached onto their surface or rolled intotheir surface or may have a porous surface. It is also within the scopeof this invention that baffles may be installed across the tubes tocreate turbulence or to direct the fiow of the reactants in a manneradvantageous to the cooling of the catalyst bed effluent. Shown in thedrawing is the preferred arrangement of the indirect heat exchangemeans, which consists of a large number of short bend U-tube heatexchangers, commonly referred to as hairpin-type heat exchangers,arranged in a cylindrical array around the outer edge of the centerpipevolume and adjacent to the catalyst retaining screen over substantiallyall the inner surface of the catalyst retaining screen through which thereactants pass. The surface area and the amount of cooling required isdependent upon the specific reactor usage and cannot be specifiedbriefly in a detailed manner for all possible situations. The optimumconfiguration of this heat exchange means will also be dependent on theflow rate of the material within the tubes and whether this is liquid orgas phase material. Alignment of the tubes along radial linesoriginating at the vertical axis of the reactor increases the efficiencyof this heat exchange with the catalyst bed effluent by approximatingcountercurrent flow.

Some form of distribution system is needed to pass equal quantities ofcoolant material through each of the elements comprising the heatexchange means and to collect the effluent of heat exchange means. Onepossible form, which consists of two concentric channels, is shown inthe drawing. Alternatively, these channels may be located on the bottomof the reactor, or one channel may be located on the top of the reactorand a second channel may be located on the bottom of the reactor. Thecooling medium passing through the heat exchange means may be anyavailable fluid, but it is advantageous to utilize some stream requiringa net input of heat, such as a recycle gas stream, one of the reactantsbeing fed to the reactor, a fractionation column charge stream, or as inthe preferred embodiment, the total combined reactor charge stream. Inthis manner, the conventional economizing by heat exchange of thereactor effluent with the reactor charge stream is conducted within thereactor. This heat exchange means could also be utilized to produce highpressure steam for use in this or other processes. The heat exchangemeans may be mounted on a separate closing plate bolted to the top ofthe reactor to allow relatively simple removal for maintenance orinspection.

A third specific element of our invention is a contact condensing meanslocated within the centerpipe volume of the radial flow reactor. Thecontact condensing means is preferably a cylindrical bed of aregularshaped vapor-liquid contacting media such as Berl saddles orRashing rings. The contact condensing means will normally beconcentrically located within the middle of the centerpipe volume but itis preferably located at a higher relative elevation than the catalystbed. The preferred placement is therefore as shown in the drawing withthe contact condensing means extending a sufficient distance above thetop of the annular catalyst bed. This allows the cooling of all materialwhich exits from the top catalyst bed by the countercurrent contactingof the catalyst bed effluent with the cooling liquid introduced abovethe condensing means. This insures complete condensation of the heavyhydrocarbons in the catalyst bed effluent stream.

It is not necessary for the contact condensing means to extend downwardto the bottom of the catalyst bed since vapor phase material cannot exitfrom the liquid containing bottom portion of the reactor and thereforeit forced to pass upward into the condensing means. This placementshould also prove beneficial in terms of a slightly reduced pressuredrop through the contact condensing means. The vapor-liquid contactingmedia forming the packed bed of the contact condensing means willnormally be confined by a solid vertical wall as shown in the drawing ora perforated vertical wall. This wall is either hung from the top of thereactor or supported-by braces attached to the bottom of the reactor. Itis also possible for the contact condensing means to consist of othertypes of vapor-liquid contacting materials such as perforated plates ora large number of horizontal, liquid covered slats. The term contactcondensing means as used in the appended claims is intended to includeany means by which the catalyst bed effluent stream is contacted with arelatively cool stream of liquid which causes the condensation of theheavier hydrocarbons within the catalyst bed effluent stream and theseparation of the catalyst bed effluent stream into a vapor phase and aliquid phase, irrespective of whether the liquid which causes thecooling of the catalyst bed effluent stream is formed by condensationand recirculation of a portion of the catalyst bed effluent stream orthe cooling liquid is an external material which is injected into thereactor. The contact condensing means may also include separate coolingcoils which cause condensation of a portion of the catalyst bed effluentstream and the in situ formation of a cool liquid.

There are several other elements to our invention.

First of all, there is a reactant inlet means which communicates withthe annular reactant distribution volume between the inner wall of theenclosed outer vessel and the outermost catalyst retaining screen.Several of these reactant inlet means may be located along or around theside of the vessel to aid in a more uniform distribution of thereactants through various parts of the catalyst bed. It is also possibleto use some sort of baffle-type device within the reactant distributionvolume to prevent the direct impingement of the incoming reactant streamupon the outermost catalyst retaining screen. Second, there is requireda vapor outlet means communicating with the internal volume of the outervessel at a point above the contact condensing means to effect theremoval of the uncondensed portion of the catalyst bed effluent stream.A demisting pad or screen may be placed across the opening of the vaporoutlet means to remove entrained liquid from this effluent vapor stream.Third, there is required a liquid outlet means communicating with theinternal volume of the outer vessel at a point below the contactcondensing means, and as indicated in the drawing, preferably at a pointsubstantially beblow the bottom of the catalyst bed to allow theaccumulation of a layer of liquid material within the reactor. The flowof liquid through the liquid outlet means will then be controlled byliquid level sensors contained within the reactor.

Optional elements of our invention include an inlet means and adistribution means for the cooling liquid which is normally fed to thetop of the contact condensing means. The cooling liquid inlet means is aconduit passing through the wall of the outer vessel and leading to thedistribution means. Suitable cooling liquid distribution means include agrid-like arrangement of conduits with a multitude of perforations, or anumber of spray nozzles chosen to provide a relatively uniform spreadingof the incoming cooling liquid over the packed bed or plates whichcomprise the contact condensing means. Many other structural elementsare also required, such as the disc-shaped flow directing plates shownin the drawing. These are necessary to prevent the reactant stream frombypassing the catalyst and also to prevent the catalyst bed effluentstream from bypassing the indirect heat exchange means. Other structuralelements would be required to support the different main elements suchas the indirect heat exchange means,.the contact condensing means andthe catalyst retaining screens.

Finally, there are the optional catalyst transfer conduits which passthrough the walls of the outer vessel and communicate with the one ormore of the catalyst retention volumes. It is preferred that there be alarge multitude of these catalyst transfer conduits with a firstplurality of the catalyst transfer conduits passing through the upperportion of the outer vessel and with a second plurality of catalysttransfer conduits passing.

through the lower portion of the outer vessel to allow the rapid anduniform removal and replacement of the catalyst. The catalyst transferconduits will normally be arranged in a circular pattern on the top andbottom of the reactor and consist of substantially vertical conduitswith one or more valve means to prevent the flow of catalyst andreactants. To allow the changing of catalyst while the catalyst and thereactor are at operating conditions, it is possible that the catalysttransfer conduits will connect with pressurized lock hoppers locatedabove and below the reactor. The catalyst may be purged and conditionedin the lock hopper above the reactor, and may be purged and cooledin'the lock hopper below the reactor. By having the lock hoppers at thesame pressure as the reactor before communicating them with the reactor,it is possible to drain and refill the catalyst retention volume withonly minimal flow of the reactants from the reactor.

In accordance with the description given above, our invention may bedescribed as a reactor for the catalytic conversion of hydrocarbonswhich comprises: (a) a vertically orientated, cylindrical outer vessel;(b) a first vertically orientated catalyst retaining screen, locatedwithin the outer vessel a distance inward from the inner surface of theouter vessel and defining an annular reactant distribution volumebetween the first catalyst retaining screen and the outer vessel; (c) asecond vertically orientated catalyst retaining screen located withinthe first catalyst retaining screen a distance inward from the firstcatalyst retaining screen and defining an annular catalyst retentionvolume between the first and the second catalyst retaining screens; (d)an indirect heat exchange means arranged as a vertically orientatedhollow cylinder having a cylindrical central void volume and locatedadjacent to the second catalyst retaining screen, at a distance inwardfrom the second catalyst retaining screen; (e) a contact condensingmeans located within the central void volume of the indirect heatexchange means; (f) a reactant inlet means communicating with thereactant distribution volume; (g) a vapor outlet means communicatingwith the internal volume of the outer vessel at a point located abovethe contact condensing means; and, (h) a liquid outlet meanscommunicating with the internal volume of the outer vessel at a pointlocated below the contact condensing means.

As previously mentioned, our invention can be applied to a wide varietyof processes which include the basic steps passing a vaporized reactantstream through a catalyst bed within a radial flow reactor, heatexchanging the effluent of the catalyst bed, partially condensing thisheat exchanged catalyst bed effluent and then separating the effluentinto a liquid and vapor phase. For instance, our invention may beapplied to the isomerization of normal paraffins having from four toeight carbon atoms per molecule when this process is conducted in aradial flow reactor. A typical isomerization process which may bepracticed with the process described herein is demonstrated in U.S. Pat.No. 3,283,021. The process of this invention is also adaptable to theproduction of butadiene from normal butane and for the production ofisoprene from isopentane. Another adaptable process is demonstrated inU.S. Pat. No. 2,773,01 1 wherein the removal of nitrogen compounds foraromatic containing streams is described. Still another processcomprises the production of specific Xylene isomers by the isomerizationof C aromatics as described in U.S. Pat. No. 3,078,318. An otherpetrochemical process to which our invention may be applied is thehydrogenation of aromatic hydrocarbons, such as the production ofcyclohexane from benzene. More details on exemplary hydrogenationprocesses may be obtained from U.S. Pat. Nos. 2,755,317 and 3,700,742.The production of benzene by the hydrodealkylation of alkyl aromatics asdescribed in U.S. Pat. No. 3,204,007 also contains the generic steps ofthe process of our invention.

This process may be utilized for the production of butadiene from butaneby the catalytic oxydehydrogenation of butenes. In one such process,butenes, air and steam are first passed into a reactor containing amixed oxide catalyst, the reactor effluent is then heat exchanged forthe production of high pressure steam and then condensed for theseparation of reaction products. Yet another application of our processis the vapor phase production of ethanol by the passage of ethylene,water and recycled ethylene through a bed of suitable catalyst. Thereactor effluent is cooled by heat exchange and separated into a liquidstream and a vapor stream, with the liquid being sent to a productrecovery zone. Reforming of various hydrocarbons, such as the reformingof relatively light hydrocarbons, or the reforming of naphthas foroctane number improvement or for the production of aromatics for use inthe petrochemical industries may also be aided by the improved processand apparatus of our invention. This is especially true in the newer lowpressure reforming operations, such as those utilizing several movingcatalyst beds at pressures of from 50 to 150 psig. Another specificexample of a petrochemical process suitable for practice with ourinvention is the disproportionation of alkyl aromatics, such as, thedisproportionation of a single methylbenzene to produce higher and lowermethylbenzenes, or the simultaneous production of benzene and mixedxylenes from a toluene feed stock. A combination process to which theinvention may be applied is demonstrated in U.S. Pat. No. 3,413,373.Long chain normal paraffins are dehydrogenated and then alkylated withbenzene to form a detergent precursor.

The process of our invention may be applied to the dehydrogenation ofnormal paraffins having from about five to 22 carbon atoms per molecule.The preferred embodiment of our invention is the dehydrogenation ofstraight chain normal paraffin having from five to carbon atoms permolecule to the corresponding mono-olefins. The production of thecorresponding olefin from these hydrocarbons is important because oftheir use in the manufacture of various chemical products such asdetergents, plastics, synthetic rubbers,

pharmeutical products, lubricants, drying oils, ion-exchange resins,plasticizers, solvents and perfumes. As an example, mono-olefins are ofsubstantial importance to the detergent industry for they may be reactedwith an alkylatable aromatic such as benzene to produce a product whichis transformed into a wide variety of biodegradable detergents. One suchdetergent is the alkylarylsulfonate type which is widely used today.Another large class of detergents is produced from normal mono-olefms asthe condensation products of alkyl phenols and ethylene oxide, prior towhich the alkyl phenol base is prepared by the alkylation of phenol withthese normal mono-olefins. A second example is the hydration of thesemono-olefins to produce alcohol which are useful in the production ofplasticizers for synthetic lube oils. The reaction conditions normallyemployed for the dehydrogenation of normal paraffins include atemperature of from about 800 to about 1,000F., a pressure of from about10 to about 200 psig. and a liquid hourly space velocity of about 10 to40, with a preferred range of liquid hourly space velocities being fromabout 12 to 34. The liquid hourly space velocity is defined to be theratio of the liquid phase volume at F. of the quantity of reactantspassed through the catalyst bed in one hour to the volume of thecatalyst contained within the catalyst bed.

The preferred catalyst is made in accordance with the teachings of U.S.Pat. No. 3,649,566 and therefore comprises a platinum group component, arhenium component, a Group V1 transition metal component and an alkalior alkaline earth metal component in conjunction with a porous carriermaterial. One specific example of the composition of the preferredcatalyst is a gamma-alumina carrier material containing, on an elementalbasis, about 0.05 to 1 wt.% platinum, about 0.05 to 1 wt.% rhenium,about 0.01 to 1 wt.% tungsten and about 0.1 to 5 wt.% of the alkali oralkaline earth metal. There are however a great number of othermaterials which may be successfully utilized as a catalyst in thedehydrogenation of paraffins. For example, tin may be substituted forgermanium in the composition given above. Other catalysts known to theart include arsenic antenuated platinum supported on a lithiated aluminaas described in U.S. Pat. No. 3,448,165, and the catalytic materialsdescribed in U.S. Pat. No. 3,647,91 1, which are comprised of a metalliccomponent selected from the group consisting of arsenic, antimony andbismuth in from about 0.15 to about 0.45 atomic ratio with a noble metalof Group VIII and from about 0.01 to about 1.5 wt.% lithium compositedwith a non-acidic inorganic oxide carrier material. The material chosenas the catalyst should be non-acidic to prevent its catalysis of thepolymerization of the olefins formed within the catalyst bed.

The primary advantage of the present invention is the reduction in theutility costs of operating the process. When applied to the illustratedpreferred embodiment, the use of a contact condenser located within thereactor results in the reduction of the pressure drop through the entireprocess of about 4 psig. The placement of the indirect heat exchangemeans within the reactor also produces a reduction in the pressure dropthrough the system of about 4 to 5 psig. By the practice of the presentinvention, it is therefore possible to acquire a horsepower savings offrom about 10 to about 16 percent at the preferred operating conditions.A second advantage of the present invention is the reduction of thecapital costs of the equipment necessary for practicing ers both theoperating and the capital costs of the chosen process.

In the operation of the process of our invention, it is preferred thatthe liquid effluent material which is removed from the bottom of thereactor is divided into a first portion which is cooled and passed intothe top of the reactor as the cooling liquid used in the contactcondensing means and a second portion which is passed to a productrecovery zone. The amount of material withdrawn as the cooling, orpump-around, liquid will be determined by optimizing such factors as theutilities cost to pump this material and the utilities cost to cool thismaterial to different temperatures. The product recovery zone mayconsist of a fractionation zone, a liquid-liquid extraction zone or asolid adsorption zone employing molecular sieves. ln the'preferredhydrogenation process, the range in the number of carbon atoms permolecule in the feed stream is held to within 4 or 5. This material ispassed through the catalyst bed and the other steps of the process inthe manner already described and the reactor effluent is then passedinto a stripping column wherein light materials formed in the process,such as light paraffins, are removed. The remaining portiori of theliquid reactor effluent material is then passed into the productrecovery zone. When the dehydrogenation process is integrated with adetergent alkylation process, the stripped reactor effluent is passeddirectly into the alkylation unit and the olefins are consumed'in thealkylation reaction. The alkylate is then recovered by fractionation andthe unconverted normal paraffins are recycled to the dehydrogenationunit. The preferred embodiment may therefore be described as a processfor the catalytically promoted dehydrogenation of normal paraffinshaving from five to carbon atoms per molecule which comprises the stepsof: (a) mixing a hydrocarbon feed stream comprising normal paraffinshaving from five to 20 carbon atoms per molecule with a recycle gasstream to form a combined feed stream; (b) passing the combined feedstream through an indirect heat exchange means having a cylindricalconfiguration and located within a radial flow reactor to effect aheating of the combined feed stream; (c) passing the combined feedstream through a heater to effect a further heating of the combined feedstream; (d) passing the combined feed stream into the radial flowreactor and through a cylindrical bed of solid catalyst to form acatalyst bed effluent stream; (e) contacting the catalyst bed effluentstream with the indirect heat exchange means located within the radialflow reactor to effect a cooling of the catalyst bed effluent stream;(f) passing the catalyst bed effluent stream into a contact condensingmeans located within the indirect heat exchange means to effeet apartial condensation and a separation of the catalyst bed effluentstream into an effluent vapor stream and an effluent liquid streamcomprising normal paraffins and mono-olefins having from five to 20carbon atoms per molecule; (g) withdrawing the effluent vapor streamfrom the radial flow reactor and returning effluent vapor streammaterial as at least a portion of the recycle gas stream; and, (h)withdrawing the effluent liquid stream from a lower portion of theradial flow reactor, and dividing the effluent liquid stream into afirst portion which is cooled by indirect heat exchange and returned tothe radial flow reactor as a cooled liquid stream fed to the contactcondensing means to effect the partial condensation of the partialcondensation of the catalyst bed effluent stream and a second portionwhich is withdrawn as a product stream.

EXAMPLE To aid in understanding the invention, a detailed description ofthe preferred embodiment, a fixed-bed catalytic process for productionof normal mono-olefins by the dehydrogenation of the correspondingparaffins, will be described. The hydrocarbon feed stream is composed ofa 10,733 lb./hr. paraffin charge stream and an 81,958 lb./hr. stream ofparaffins recycled from a detergent alkylation zone. These materials arecombined and pressurized to form a liquid'feed stream at 410F. and 54psig. A l-6,277 lb./hr. recycle gas stream at a temperature of 22F. and55 psig. is combined with the liquid feed stream to form a mixed-phasecombined feed stream having an average temperature of 303F. The exactcompositions of these streams and those later referred to herein aregiven in Table l in moles/- hour.

The combined feed stream is fed into a feed-effluent heat exchange meanslocated within the reactor. This heat exchange means consists of a largenumber of U- tubes in a circular array around the inside of theinnermost catalyst retaining screen. The radial flow reactor is about 7feet in diameter inside and the catalyst bed contained therein is 9inches thick. The combined feed stream is completely vaporized withinthe heat exchange means due to its increase in temperature to 751F., andits pressure is reduced to 39 psig. Three pounds per hour of water areinjected at this point, and the combined feed stream is then passedthrough a direct fired heating means which further heats the material to930F. before it is charged to the reactor at 35 psig. Passage of theheated combined feed stream through the catalyst bed under theseconditions, including a combined feed liquid hourly space velocity of28, causes the dehydrogenation of approximately 8-13 percent of thevarious paraffins into mono-olefins and results in the production of acorresponding amount of hydrogen. Some iso-olefins and diolefins arealso produced.

The effluent stream of the catalyst bed enters the centerpipe volume ofthe reactor at a temperature of about 898F. and a pressure of about 30psig. lt very quickly impinges upon the adjacent U-tubes of theeffluent-feed heat exchange means and is reduced in temperature to about403F. After contacting the heat exchange means, the catalyst bedeffluent is passed into a packed contact condenser wherein it is cooledand partially condensed. This cooling and condensation is caused by a186,617 lbi/hr. pump-around stream of reactor effluent liquid which hasbeen withdrawn from the reactor and cooled to F. before it isdistributed over thetop of the contact condenser. The material condensedto form the reactor effluent liquid is the C to C paraffins and olefinsin the catalyst bed effluent stream. The uncondensed reactor effluentvapor stream is mainly hydrogen with small amounts of various C to Chydrocarbons and a slight amount of the heavier C to C materials. Thereactor effluent vapor stream is removed from a top portion of thereactor at a point over the contact condenser at a pressure of about 27psig. and a temperature of about ll 50F. A small slip stream of this gascomprising 205 lbs/hr. is diverted to a desulfurization process toutilize the hydrogen formed in the process. The remainingportion of theeffluent vapor stream is used as the recycle gas stream previouslymentioned. The reactor effluent liq uid stream is accumulated in thebottom of the reactor and withdrawn at 334F. and about 27 psig. Thepumparound cooling liquid is withdrawn, and the remaining 92,493 lb./hr.liquid stream is passed into a stripping column, which functions as theproduct recoveryzone and operates wtih a bottom temperature of 495F. at28 psig. This produces a 92,297 lb./hr. bottoms stream which is passedinto the detergent alkylation zone.

14 5. The process of claim lfurther characterized in that the processcomprises the hydrodealkylation of aromatic hydrocarbons having fromseven to 11 carbon atoms per molecule.

6. The process of claim 1 further characterized in that the processcomprises the hydrogenation of aromatic' hydrocarbons.

7. The process of claim 1 further characterized in that the processcomprises the disproportionation of alkyl aromatics.

8. The process of claim 1 further characterized in that the processcomprises the removal of sulfur and nitrogen compounds from ahydrocarbon stream containing aromatic hydrocarbons.

9. The process of claim 1 further characterized in that said coolingfluid comprises at least a portion of said hydrocarbon feed stream.

TABLE 1' HOURLY FLOW RATES 1N MOLES PER HOUR Contact Contact Pump FreshParaffin Recycle Reactor Condenser Condenser Around Feed Recycle GasEffluent Gas Liquid Liquid 4427.12 4484.66 4482.97 5.10 3.41 H., C,41.22 41.78 41.74 0.11 0.07 C; 95.91 97.34 97.12 0.64 0.42 C; 23.7824.21 24.08 0.39 0.26 C; 18.23 18.64 18.46 0.52 0.34 C 11.10 11143 11.240.58 0.39 G C 1.00 1.82 1.02 2.44 1.63 nParaffins C 0.22 0.01 0.21 0.010.60 0.40 C 25.73 214.31 2.38 221.55 2.40 661.31 442.17 C 20.90 156.240.66 160.35 0.67 481.87 322.19 C 12.31 80.87 0.14 82.79 0.14 249.42166.77 C 3.20 18.75 0.01 19.18 0.01 57.85 38.68 Cyclic Paraffins 0.535.67 0.02 5.84 0.02 17.56 11.74 lsoparaffins 0.41 4.94 0.04 5. 0 0.0415.27 10.21 Aromatics 0.34 8.97 0.04 10.92 0.04 32.83 21.95

Oleflns C 0.01 0.03 0.02 C 0.24 19.38 0.25 57.76 38.62 C 0.08 15.85 0.0847.59 31.82 Cm 0.02 9.37 0.02 28.22 18.87 C 2.43 7.33 4.90 CyclicOlefins 0.37 1.12 0.75 lso-olefins 0.44 1.33 0.89 Diolefins 0.01 2.050.01 6.16 4.12 Total 63.64 489.75 4636.30 5250.19 4694.79 1676.031120.62 1b./hr. 10733 81958 16277 108971 16483 279110 186617 We claim asour invention: 10. The process of claim 1 further characterized in l. Ahydrocarbon conversion process which comprises the steps of:

a. passing a hydrocarbon feed stream at conversion conditions radiallythrough a bed of conversion catalyst in a radial flow reactor;

b. passing the resultant conversion product effluent from the catalystbed in-indirect heat exchange with a cooling fluid within said reactor;and

then passing the resultant cooled effluent into a solid contact materialdisposed within said reactor at conditions effecting partialcondensation and separation of the effluent into a vapor phase and aliquid phase, whereby the pressure drop within the process is reducedand the degradation within the reactor of hot conversion products isreduced.

2. The process of claim 1 further characterized in that the processcomprises the reforming of a naphtha.

3. The process of claim 1 further characterized in that the processcomprises the isomerization of normal paraffins having from four toeight carbon atoms per molecule.

4. The process of claim 1 further characterized in that the processcomprises the isomerization of C aromatics to produce specific Xyleneisomers.

that said cooling fluid comprises at least a portion of said hydrocarbonfeed stream and a recycle gas stream separated from said vapor phase.

11. The process of claim 1 further characterized in that a portion ofsaid liquid phase is cooled and returned to the radial flow reactor tocool said solid contact material.

12. A process for the catalytic conversion of hydrocarbons whichcomprises the steps of:

a. passing at least a portion of a hydrocarbon feed stream in indirectheat exchange with hot conversion products within a radial flow reactorto effect a heating of this portion of the feed stream;

b. further heating the feed stream to vaporize the same;

0. passing the resultant vapors into the radial flow reactor and througha cylindrical bed of solid catalyst therein to form a catalyst bedeffluent stream;

d. passing the catalyst bed effluent stream to said indirect heatexchange step to effect a cooling of the catalyst bed effluent stream;

e. passing the cooled catalyst bed effluent steam into a bed of solidcontact material located within the radial flow reactor to effect apartial condensation 1 5 and a separation of the catalyst bed effluentstream into an effluent vapor stream and an effluent liquid stream; and,I

f. withdrawing the effluent liquid stream from the radial flow reactorand cooling and returning a portion thereof to the radial flow reactorinto contact with said solid contact material to effect the partialcondensation of the catalyst bed effluent stream.

13. A process for the catalytically promoted dehydrogenation of normalparaffins having from five to 20 carbon atoms per molecule whichcomprises the steps of:

a. mixing a hydrocarbon feed stream comprising normal paraffins havingfrom five to 20 carbon atoms per molecule with a recycle gas stream toform a combined feed stream;

b. passing the combined feed stream in indirect heat exchange with hotcatalyst bed effluent within a radial flow reactor to effect a heatingof the combined feed stream;

0. further heating the combined feed stream to vaporize the same;

d. passing the resultant vapors into the radial flow reactor and througha cylindrical bed of solid catalyst to form a catalyst bed effluentstream;

e. passing the catalyst bed effluent stream to said indirect heatexchange step to effect a cooling of the catalyst bed effluent stream;

f. passing the cooled catalyst bed effluent stream into a bed of solidcontact material located Within the radial flow reactor to effect apartial condensation and a separation of the catalyst bed effluentstream into an effluent vapor stream and an effluent liquid streamcomprising normal paraffms and mono-olefins havng from 5 to 20 carbonatoms per molecule;

g. withdrawing the effluent vapor stream from the radial flow reactorand returning a portion thereof as at least a portion of the recycle gasstream; and,

h. withdrawing the effluent liquid stream from a lower portion of theradial flow reactor, and dividing the effluent liquid stream into afirst portion which is cooled by indirect heat exchange and returned tothe radial flow reactor as a cooled liquid stream fed into contact withsaid solid material to effect the partial condensation of the catalystbed effluent stream and a second portion which is withdrawn as a productstream.

1. A HYDROCARBON CONVERSION PROCESS WHICH COMPRISES THE STEPS OF: A.PASSING A HYDROCARBON FEED STREAM AT CONVERSION CONDITIONSRADIALLYTHROUGH A BED OF COONVERSION CATALYST IN A RADIAL FLOW REACTOR, B.PASSING THE RESULTANT CONVERSION PRODUCT EFFLUENT FROM THE CATALYST BEDIN INDIRECT HEAT EXCHANGE WITH A COOLING FLUID WITHIN SAID REACTOR, ANDC. THEN PASSING THE RESULTANT COOLED EFFLUENT INTO A SOLID CONTACTMATERIAL DISPOSED WITHIN SAID REACTOR AT CONDITIONS EFFECTING PARTIALCONDENSATION AND SEPARATION OF THE EFFLUENT INTO A VAPOR PHASE AND ALIQUID PHASE, WHEREBY THE PRESSURE DROP WITHIN THE PROCESS IS REDUCEDAND THE DEGRADATION WITHIN THE REACTOR OF HOT CONVERSION PRODUCTS ISREDUCED.
 2. The process of claim 1 further characterized in that theprocess comprises the reforming of a naphtha.
 3. The process of claim 1further characterized in that the process comprises the isomerization ofnormal paraffins having from four to eight carbon atoms per molecule. 4.The process of claim 1 further characterized in that the processcomprises the isomerization of C8 aromatics to produce specific xyleneisomers.
 5. The process of claim 1 further characterized in that theprocess comprises the hydrodealkylation of aromatic hydrocarbons havingfrom seven to 11 carbon atoms per molecule.
 6. The process of claim 1further characterized in that the process comprises the hydrogenation ofaromatic hydrocarbons.
 7. The process of claim 1 further characterizedin that the process comprises the disproportionation of alkyl aromatics.8. The process of claim 1 further characterized in that the processcomprises the removal of sulfur and nitrogen compounds from ahydrocarbon stream containing aromatic hydrocarbons.
 9. The process ofclaim 1 further characterized in that said cooling fluid comprises atleast a portion of said hydrocarbon feed stream.
 10. The process ofclaim 1 further characterized in that said cooling fluid comprises atleast a portion of said hydrocarbon feed stream and a recycle gas streamseparated from said vapor phase.
 11. The process of claim 1 furthercharacterized in that a portion of said liquid phase is cooled andreturned to the radial flow reactor to cool said solid contact material.12. A process for the catalytic conversion of hydrocarbons whichcomprises the steps of: a. passing at least a portion of a hydrocarbonfeed stream in indirect heat exchange with hot conversion productswithin a radial flow reactor to effect a heating of this portion of thefeed stream; b. further heating the feed stream to vaporize the same; c.passing the resultant vapors into the radial flow reactor and through acylindrical bed of solid catalyst therein to form a catalyst bedeffluent stream; d. passing the catalyst bed effluent stream to saidindirect heat exchange step to effect a cooling of the catalyst bedeffluent stream; e. passing the cooled catalyst bed effluent steam intoa bed of solid contact material located within the radial flow reactorto effect a partial condensation and a separation of the catalyst bedeffluent stream into an effluent vapor stream and an effluent liquidstream; and, f. withdrawing the effluent liquid stream from the radialflow reactor and cooling and returning a portion thereof to the radialflow reactor into contact with said solid contact material to effect thepartial condensation of the catalyst bed effluent stream.
 13. A processfor the catalytically promoted dehydrogenation of normal paraffinshaving from five to 20 carbon atoms per molecule which comprises thesteps of: a. mixing a hydrocarbon feed stream comprising normalparaffins having from five to 20 carbon atoms per molecule with arecycle gas stream to form a combined feed stream; b. passing thecombined feed stream in indirect heat exchange with hot catalyst bedeffluent within a radial flow reactor to effect a heating of thecombined feed stream; c. further heating the combined feed stream tovaporize the same; d. passing the resultant vapors into the radial flowreactor and througH a cylindrical bed of solid catalyst to form acatalyst bed effluent stream; e. passing the catalyst bed effluentstream to said indirect heat exchange step to effect a cooling of thecatalyst bed effluent stream; f. passing the cooled catalyst bedeffluent stream into a bed of solid contact material located within theradial flow reactor to effect a partial condensation and a separation ofthe catalyst bed effluent stream into an effluent vapor stream and aneffluent liquid stream comprising normal paraffins and mono-olefinshavng from 5 to 20 carbon atoms per molecule; g. withdrawing theeffluent vapor stream from the radial flow reactor and returning aportion thereof as at least a portion of the recycle gas stream; and, h.withdrawing the effluent liquid stream from a lower portion of theradial flow reactor, and dividing the effluent liquid stream into afirst portion which is cooled by indirect heat exchange and returned tothe radial flow reactor as a cooled liquid stream fed into contact withsaid solid material to effect the partial condensation of the catalystbed effluent stream and a second portion which is withdrawn as a productstream.